This invention relates to an intake system and more particularly to an improved induction system for an internal combustion engine.
As is well known, the induction system of an internal combustion engine is extremely important in determining the performance of the engine. Since in many applications, particularly for use in motor vehicles, the engine is required to run over widely varying speed and load ranges, it has been proposed to provide an induction system wherein each cylinder of the engine is served by a pair of intake passages each of which is tuned for a different running condition of the engine. Such an arrangement is shown in U.S. Pat. No. 4,649,876, entitled "Intake Means of Internal Combustion Engine," issued Mar. 17, 1987 in the names of Masatoshi Ohmi, et al., which patent is assigned to the assignee hereof. That induction system is particularly designed for use with V-type engines and includes a pair of plenum chambers each disposed in proximity to one of the cylinder banks. The two intake passages for each cylinder are served respectively by one of the plenum chambers so as to provide a short high-speed intake passage from the adjacent plenum chamber and a longer low-speed intake passage from the plenum chamber associated with the opposite cylinder bank. This arrangement provides extremely good engine performance.
However, the arrangement used therein requires a number of intake passages that extend across the valley between the cylinder banks to the opposite plenum chambers. This adds significantly to the external plumbing of the engine. In addition, this type of induction system generally increases the height requirements of the engine, not always a desirable result.
It is, therefore, a principal object of this invention to provide an improved induction system for an engine that permits tuning of the cylinder to two different speed ranges while at the same time maintaining a minimum amount of external plumbing and a low height.
The amount of external conduitry required can be simplified if not all cylinders of each cylinder bank are served by the plenum chambers of both cylinder banks. However, if one plenum chamber serves both intake passages for the cylinder of the associated cylinder bank, it is somewhat more difficult to provide the different flow lengths to provide the different tuning.
It is, therefore, a further object of this invention to provide an improved induction system for an engine having cylinder banks which reduces the number of external conduits but which permits independent tuning of two intake passages for each cylinder.
If both intake passages of a given cylinder are served by an adjacent plenum chamber or, for that matter, by a plenum chamber disposed on the opposite side of the engine, then a situation may arise wherein the intake pulses from one cylinder adversely effect those of other cylinders. In U.S. Pat. No. 4,809,647, entitled "Intake System for Multi-Cylindered Engine," issued Mar. 7, 1989 in the name of Iwao Matsumoto, et al., assigned to the assignee hereof, there is disclosed an arrangement wherein the cylinders of the engine fire in an order so that no two cylinders will draw from the same plenum chamber on successive firings. This improves the performance of the engine because it ensures that adequate air will be available in each plenum chamber to serve the cylinders.
Such an arrangement is facilitated when each cylinder has both of its intake passages served by a different plenum chamber. However, when one plenum chamber may serve both intake passages of the same cylinder, then it is more difficult to ensure that no two cylinders will draw successively from the same plenum chamber.
It is, therefore, a still further object of this invention to provide an improved induction system for an internal combustion engine having a pair of plenum chambers that serve a multitude of cylinders and wherein the charge is not drawn from one plenum chamber on successive firings of the engine under at least certain running conditions.
As will be noted from the aforenoted United States Letters Patents, the system can be simplified if there is a single atmospheric air inlet that serves both plenum chambers. This eliminates the necessity for separate air cleaner, silencer assemblies for each plenum chamber and also permits the use of a single main throttle valve positioned in the common air inlet. However, this generally requires the inlets to the respective plenum chambers to be located at one end of the engine so as to reduce height and avoid additional complexity of the intake plumbing. However, when the air is introduced into the plenum chamber at one of its ends, then different air flow lengths occur between the inlet and the various cylinders served by them. This can cause some cylinder to cylinder variation.
It is, therefore, a still further object of this invention to provide an improved induction system for a plenum chamber that serves a multiple number of cylinders and which has its inlet at one end but which minimizes the difference of the flow lengths between the inlet and the individual cylinders served thereby.
The problem of maintaining a low hoodline has already been mentioned in conjunction with induction systems of this type. By positioning the plenum chambers over the cylinder heads of the engine, the height of the induction system is increased. Where the engine is positioned transversely in the engine compartment, a common practice with certain types of vehicles such as front engine, front wheel drive or rear engine, rear wheel drive vehicles, the desire of providing a sloping hood can be complicated by this type of induction system.
It is, therefore, a still further object of this invention to provide an induction system of this type which maintains a low engine profile and permits a low sloping hood.